JP2003200469A - Control device of injection drive part of motor-driven injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate a deviation between an injection speed and an injection pressure due to an electrical and a mechanical dispersion between one threaded shaft drive system and the other. <P>SOLUTION: This control device comprises a speed control manipulated variable arithmetic means 33 which calculates a speed control manipulated variable for making an injection speed coincide with a target injection speed, a pressure control manipulated variable arithmetic means 36 which calculates a pressure control manipulated variable for making the injection pressure coincide with the target injection pressure, a pressure deviation means 22 which detects a deviation between pressurizing forces to be applied to a mobile frame 6 by rotation of a first and a second ball and threaded shaft 8A and 8B during an injection step, a splitting means 37 which splits the pressure control manipulated variable to form the first and second 1/2 pressure control manipulated variables and a correcting means 51 which corrects the first 1/2 pressure control manipulated variable by a deviation between the pressurizing forces. Thus it is possible to inhibit a pressure deviation by correction of the first 1/2 pressure control manipulated variable based on the deviation between the pressurizing forces. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric injection drive device in an injection molding machine.

[0002]

2. Description of the Related Art In a conventional electric injection drive device of an electric injection molding machine, screw shafts are provided at symmetrical positions sandwiching an injection screw, and these screw shafts are respectively screwed into nuts fixed to a moving frame. . Each screw shaft is synchronously driven by an individual servo motor directly connected to them,
As a result, the injection screw attached to the moving frame is moved back and forth. In such an injection molding machine, in order to prevent the overload of the motor, the resin pressure at the time of injection is measured, and when this resin pressure exceeds the standard,
It is necessary to take protective measures such as lowering the injection speed.

Therefore, in the electric injection molding machine disclosed in JP-A-62-218118, the injection pressure is detected by a strain gauge provided at the joint between the nut and the moving frame, and based on this injection pressure. By controlling the servo motor, the overload of the servo motor is prevented.

Further, in the conventional example disclosed in Japanese Unexamined Patent Publication No. 10-113970, the operation amount corresponding to the deviation between the injection set pressure and the actual injection pressure is P in the injection filling step.
The injection speed command value calculated based on the output of the PID calculation unit is clamped to the injection speed set value to suppress the injection speed in the first half of the injection process.

Further, in the conventional example disclosed in Japanese Patent Laid-Open No. 11-28751, a motion controller drives a master servo motor for operating an injection screw via a master servo amplifier. The master servo amplifier includes a torque command calculator that calculates a torque command signal.
The torque command calculation unit commands the drive torque of the master servo motor and at the same time transmits the drive torque command of the slave servo motor to the slave servo amplifier, and the slave servo amplifier drives the slave servo motor by this drive torque command. In this way, the plurality of injection drive motors are synchronously controlled.

[0006]

Problems to be Solved by the Invention JP-A-62-2181
The techniques disclosed in Japanese Patent Laid-Open No. 18 and Japanese Patent Application Laid-Open No. H10-113970 are based on the assumption that the motor torques for generating rotation and injection pressure of each screw shaft are perfectly synchronized. However, when a pair of screw shafts installed in parallel on both sides of the injection screw are driven by the corresponding servo motors, the electrical and mechanical between the servo motors in one and the other screw shaft drive system The injection speed and the injection pressure may deviate from the respective target values due to such variations and mechanical variations between the screw shafts. Further, the technique disclosed in Japanese Patent Application Laid-Open No. 11-28751 cannot deal with the deviation of the injection speed and the injection pressure due to the mechanical variation between the screw shafts.

The present invention has been made in view of such problems, and it is possible to eliminate the deviation between the injection speed and the injection pressure due to the electrical and mechanical variations between the one and the other screw shaft drive systems. An object of the present invention is to provide a control device for an injection drive unit in a possible electric injection molding machine.

[0008]

DISCLOSURE OF THE INVENTION The present invention is directed to an injection cylinder in which an injection screw is fitted in a retractable manner, and first and second balls provided so as to be symmetrically parallel to each other about an axis of the injection cylinder and rotatable. A fixed frame to which a screw shaft and first and second drive motors that rotate and drive the first and second ball screw shafts are attached respectively, and the fixed frame is located behind the fixed frame and includes the first and second First and second ball screw nuts respectively screwed to the ball screw shaft, the injection screw, and a moving frame to which a third drive motor for rotationally driving the injection screw is attached, and the first and second A control device applied to control of an injection drive unit of an electric injection molding machine configured to move the moving frame together with the injection screw in a straight line by the synchronous rotation of the ball screw nut. Speed control operation amount calculation means for calculating a speed control operation amount for matching the speed with the target injection speed; and pressure control operation amount calculation means for calculating a pressure control operation amount for matching the injection pressure with the target injection pressure. A pressure deviation output means for detecting a deviation of each pressing force applied to the moving frame by the rotation of the first and second ball screw shafts during the injection step; A dividing means for forming a second ½ pressure control operation amount, a correcting means for correcting the first ½ pressure control operation amount by a deviation of each pressing force, the speed control operation amount and the First output means for outputting a current corresponding to the smaller operation amount of the corrected first 1/2 pressure control operation amount to the first drive motor, the speed control operation amount, and the first output means. 2 of 1/2 pressure control manipulated variable Second outputting a current corresponding to the operation amount of the again side to the second drive motor
Output means for suppressing the pressure deviation by correcting the first ½ pressure control operation amount based on the deviation of each of the applied pressures.

In an embodiment of the present invention, the pressure deviation detecting means is configured to detect the pressure deviation based on the difference in the number of rotations of the first and second ball screw shafts.

Further, in the embodiment of the present invention, in order to detect the injection pressure, first and second pressure detection sensors for respectively detecting tensile forces acting on the first and second ball screw shafts are provided. , And adding means for adding the pressures detected by these sensors.

Further, in the embodiment of the present invention, in order to detect the injection pressure, a pressure detection sensor for detecting a tensile force acting on the first ball screw shaft, and the first and the first from the injection cylinder. The distance to the ball screw axis of 2 is l ₁ ,
As l ₂ , the pressure detected by the pressure sensor is (l ₁ +
l ₂ ) / l ₁ multiplication means is provided.

The present invention is a control device applied to the control of an injection drive unit of the electric injection molding machine, wherein a speed control operation amount for calculating a speed control operation amount for matching an injection speed with a target injection speed. A calculation means, a pressure control operation amount calculation means for calculating a pressure control operation amount for matching the injection pressure with the target injection pressure, and a rotation speed difference between the first and second ball screw shafts during the injection process. And a dividing means for dividing the pressure control operation amount into two to form first and second 1/2 pressure control operation amounts, and the speed control operation amount is corrected by the rotation speed difference. Correction means and a first output for outputting to the first drive motor a current corresponding to a smaller operation amount of the first 1/2 pressure control operation amount and the corrected speed control operation amount. Means and the second 1 /
Two pressure control operation amounts and second output means for outputting a current corresponding to the smaller operation amount of the speed control operation amounts to the second drive motor, and the second output unit based on the rotational speed difference. The rotation speed difference is suppressed by correcting the speed control operation amount of 1.

In the embodiment of the present invention, in order to detect the injection pressure, first and second pressure detection sensors for detecting tensile forces acting on the first and second ball screw shafts, respectively, and these And an adding means for adding the pressure detected by the sensor.

Further, in the embodiment of the present invention, in order to detect the injection pressure, a pressure detection sensor for detecting a tensile force acting on the first ball screw shaft, and the first and the first from the injection cylinder. The distance to the ball screw axis of 2 is l ₁ ,
As l ₂ , the pressure detected by the pressure sensor is (l ₁ +
l ₂ ) / l ₁ multiplication means is provided.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the first of the present invention.
FIG. 3 is a plan view showing a partial cross section of the injection drive unit 1 of the electric injection molding machine according to the embodiment of FIG. This injection drive unit 1
Is a fixed frame 2 fixed to a main body not shown.
And a moving frame 6 that moves so as to be able to come into contact with and separate from the fixed frame 2.

The fixed frame 2 is provided with a center hole extending in the horizontal direction, and the base of the injection cylinder 3 is passed through the center hole. The injection cylinder 3 is fixed to the frame 2 by a retaining ring 5 provided on the front side surface of the fixed frame 2, and an injection screw 4 is fitted to the inner periphery of the fixed frame 2 so as to be rotatable and movable back and forth. Injection driving reduction motors 11A and 11B are attached to the fixed frame 2 at symmetrical positions about the axis of the injection screw 4, and the ball screw shafts 8A and 8B are provided inside the motors 11A and 11B.
Are arranged in parallel.

The ball screw shafts 8A, 8B are provided at symmetrical positions with respect to the axis of the injection screw 4, and are rotatably supported by the fixed frame 2 via bearings 9A, 9B, respectively. The bearings 9A and 9B are configured to be able to receive a large thrust load. Motor 11
The driving forces of A and 11B are respectively the toothed belt 13
And the toothed belt pulleys 14 and 15 are transmitted to the ball screw shafts 8A and 8B while being decelerated through the power transmission means.

At the shaft ends of the ball screw shafts 8A, 8B, encoders 16A,
16B is installed. In addition, a hopper (not shown) into which pellets of resin, which is a raw material for molding, is placed is installed at substantially the center of the upper surface of the fixed frame 2. A ball screw shaft 8A is provided on one side and the other side of the moving frame 6.
Ball screw nuts 17A and 17B that are screwed into the male balls 8a and 8b of the ball screw 8B and 8B, respectively, are arranged. At the center of the moving frame 6, a screw rotation drive motor 7 that rotationally drives the injection screw 4 is attached. Has been.

The pair of injection drive motors 11A and 11B
Is rotated synchronously, the ball screw shafts 8A and 8B rotate, and the rotary motion is converted into a rectilinear motion of the moving frame 6. At the time of injection molding described later, the injection screw 4 moves forward together with the moving frame 6 by the rotation of the ball screw shafts 8A and 8B. The injection screw 4 is rotationally driven by the screw rotation drive motor 7. The drive side end of the injection screw 4 is supported by a large-capacity thrust bearing (not shown) built in the moving frame 6. Therefore, the injection screw 4 can freely rotate even in the state of receiving a large ejection force.

Pressure detection sensors (for example, load cells) 18A and 18B are fixed to the moving frame 6.
These pressure detection sensors 18A and 18B detect the axial forces that the ball screw nuts 17A and 17B receive from the ball screw shafts 8A and 8B, respectively. When the injection screw 4 is ejected and moved, the pressure detection sensor 18A,
The sum of the detected pressures of 18B corresponds to the injection pressure. This pressure detection sensor 18A, 18B
Is connected to the control device 30 shown in FIG. 2 via signal lines 22A and 22B.

By the way, the pair of ball screw shafts 8A,
When 8B rotates in perfect synchronization, it is possible to detect the injection pressure using only one of the pressure detection sensors 18A and 18B. That is, for example, when only the pressure detection sensor 18A is used for detection, the distances between the ball screw shafts 8A and 8B and the center axis of the injection screw 4 are set to l ₁ and l ₂ , respectively, and the pressure detection sensor 18A is set. The injection pressure can be detected by multiplying the output of (1 ₁ + l ₂ ) / l ₁ . When the above method is adopted, the adder 35 is replaced by an operation means for executing the operation (l ₁ + l ₂ ) / l ₁ .

When the distances l ₁ and l ₂ are equal, (l ₁ + l ₂ ) / l ₁ = 2, so the injection pressure is detected by doubling the output of the pressure detection sensor 18A. be able to. When one pressure sensor (sensor 18A in the above example) is used as described above, the pressure sensor on the other side (sensor 18A in the above example) is used.
Instead of B), a dummy of the same shape made of the same material may be provided.

Next, the configuration of the control device 30 will be described with reference to FIG. In the control device 30, the screw shaft position deviation calculator 31 calculates the rotational speed difference between the ball screw shafts 8A and 8B based on the outputs of the encoders 16A and 16B, and based on the rotational speed difference, the ball screw nut 17A and the ball screw nut 17A. The position offset amount of the nut 17B is calculated.

The pressure deviation calculating circuit 32 calculates the deviation of each injection direction pressure generated by the rotation of the ball screw shafts 8A and 8B based on the position offset amount. The injection pressure setting device 38 sets a target injection pressure, and the injection speed setting device 34 sets a target injection speed corresponding to the target injection pressure.

The injection speed setting unit 34 stores the relationship between the injection stroke position and the target injection speed V as illustrated in FIG. 4, and this relationship and an injection stroke sensor (moving position of the moving frame 6) not shown in the drawing are stored. The target injection speed V corresponding to the stroke position is set based on the injection stroke position of the injection screw 4 detected by the (sensor for detecting). The injection pressure setter 38 stores the relationship between the injection stroke and the target injection pressure P as illustrated in FIG. 4, and this relationship and the injection stroke position of the injection screw 4 detected by the injection stroke sensor. Based on, the target injection pressure P corresponding to the stroke position is set. According to the relationship shown in FIG. 4, the low injection pressure P1 and the high injection speed V1 are set as the target injection pressure P and the target injection speed V, respectively, in the injection filling zone, and the high injection pressure P2 and almost 0 are set in the pressure holding zone. Are set as the target injection pressure P and the target injection speed V, respectively.

The injection speed PID control circuit 33 uses the target injection speed V and the rotational speed of the ball screw shaft 8 detected by either one of the encoders 16A and 16B (encoder 16A in this example) (actual injection speed). Corresponding to)
Calculate the speed control manipulated variable corresponding to the deviation between and.

The pressure adder 35 includes a pressure detection sensor 18
The respective pressures detected by A and 18B (tensile forces acting on the screw shafts 8A and 8B) are added, and the addition result (actual injection pressure) is applied to the injection pressure PID control circuit 36. The injection pressure PID control circuit 36 calculates a pressure control operation amount corresponding to a deviation between the target injection pressure P and the addition result. The divider 37 divides the pressure control operation amount output from the pressure PID control circuit 36 into two, and outputs one of the divided outputs to the adder 51.
To the output circuit 39B.
Output to. The adder 51 adds the injection pressure deviation output from the pressure deviation calculation circuit 32 to the 1/2 pressure control operation amount output from the divider 37.

The output circuit 39A adds the speed control operation amount output from the injection speed PID control circuit 33 and the adder 5
The addition result of 1 is input, and the current defined by them is output to the motor 11A. On the other hand, the output circuit 39B
Inputs the speed control operation amount output from the injection speed PID control circuit 33 and the 1/2 pressure control operation amount output from the divider 37, and outputs a current defined by them to the motor 11B.

In FIG. 1, the solid line shows a state in which the moving frame 6, the screw rotation drive motor 7, the ball screw nuts 17A and 17B, etc. are at the forward end positions after the injection process is completed. After this state is reached, the resin feeding and plasticizing steps are started. Also, FIG.
In Fig. 2, the chain double-dashed line indicates a state in which the injection resin 4, the moving frame 6, the screw rotation drive motor 7, and the ball screw nuts 17A and 17B are located at the reverse end after the molten resin has been accumulated at the tip of the injection cylinder 3. Is shown.

In the resin feeding and plasticizing process by the injection cylinder 3 and the injection screw 4, resin pellets are injected from the hopper (not shown) by the rotation of the injection screw 4 by the screw rotation drive motor 7.
Will be introduced in. This resin pellet is melted and plasticized by being heated while being sent forward by the screw 4. On the other hand, in this resin feeding and plasticizing process, the injection drive motor 1
Ball screw shaft 8 by low speed synchronous operation of 1A and 11B
Rotate A and 8B simultaneously at low speed. As a result, the moving frame 6 is slowly retracted from the position shown in FIG. 1 together with the injection screw 4, and as a result, the molten resin is accumulated at the tip of the injection screw 4.

When one shot of resin for a mold (not shown) is accumulated at the tip of the injection screw 4, the moving frame 6 is stopped at the position shown by the chain double-dashed line in FIG. 1, and the injection screw is rotationally driven. The motor 7 is also stopped. Next, the pair of injection drive motors 11A and 11B are rotated at high speed so that the injection screw 4 moves forward at the high speed V ₁ shown in FIG. 4, whereby the resin accumulated at the tip of the injection screw 4 is illustrated. Not injected into the mold cavity. At this time, the moving frame 6 is returned to the position indicated by the solid line in FIG. Then, thereafter, the resin feeding, the plasticizing step, and the injection step are repeated in the same manner as above.

Next, the control operation of the control device 30 will be described. During the injection process of the electric injection molding machine 1, the rotation speed of the ball screw shafts 8A and 8B detected by the encoders 16A and 16B is the screw shaft position deviation calculator 3.
Input to 1. If the rotational speeds of the ball screw shafts 8A and 8B are deviated, the positions of the ball screw nuts 17A and 17B screwed onto the ball screw shafts 8A and 8B are deviated.
Therefore, the screw shaft position deviation calculator 31 calculates the amount of position offset of the ball screw nuts 17A and 17B based on each of the rotation speeds.

The position offset amount of the ball screw nuts 17A, 17B corresponds to the deviation of each load pressure acting on the ball screw shafts 8A, 8B. Therefore, the pressure deviation calculation circuit 3
2 is preset for the above-mentioned position offset amount based on a predetermined correction coefficient (ball screw shafts 8A, 8B, ball screw nuts 17A, 17B and the shape, rigidity, clearance between the components and the like of the peripheral components. )) To calculate the deviation of each load pressure.

The load pressure deviation hinders smooth movement of the frame 6. Therefore, in this embodiment, the divider 3
The adder 51 executes a calculation for adding the load pressure deviation to one of the 1/2 pressure control manipulated variables output from No. 7, thereby correcting the 1/2 pressure control manipulated variable. As a result, the output control circuits 39A and 39B output a pressure control operation amount that makes the load pressure deviation zero.

The output circuit 39A supplies a current corresponding to the former to the motor when the speed control operation amount output from the injection speed PID control circuit 33 is equal to or less than the corrected 1/2 pressure control operation amount output from the adder 51. 11A and outputs the current corresponding to the latter to the motor 11 when the former is larger than the latter.
Output to A. Further, the output circuit 39B has an injection speed PI.
When the speed control operation amount output from the D control circuit 33 is smaller than the 1/2 pressure control operation amount output from the divider 37, a current corresponding to the former is output to the motor 11B, and the former is larger than the latter. Sometimes the current corresponding to the latter is output to the motor 11B.

That is, the control device 30 controls the injection speed P
Corresponding to the output of the adder 51 (corrected 1/2 pressure control) in a partial period of the injection filling zone of FIG. 4 in which the speed control operation amount output from the ID control circuit 33 becomes large and the pressure increasing zone subsequent thereto A current corresponding to the manipulated variable is output from the output circuit 39A, and a current corresponding to the 1/2 pressure control manipulated variable is output from the output circuit 39B. In this case, the injection drive motors 11A and 11B are controlled so that the injection pressure becomes the target injection pressure set by the injection pressure setter 38 and the deviation of the load pressure acting on the screw shafts 8A and 8B is eliminated. Will be done.

On the other hand, the control device 30 controls the injection speed PI.
In the second half period of the pressure increasing zone and the pressure maintaining zone of FIG. 4 in which the speed control operation amount output from the D control circuit 33 decreases, currents corresponding to the speed control operation amount injection are output from the output circuits 39A and 39B, respectively. . In this case, the injection drive motors 11A and 11B are controlled so that the injection speed becomes the target injection speed set by the injection speed setting unit 34. As a result, in the injection filling zone of FIG.
A, a driving means including a ball screw shaft 8A and the like, and a motor 11
B, ball screw shafts 8A, 8B, etc. due to electrical and mechanical variations between the driving means including the ball screw shaft 8B and the like.
The imbalance of the tensile force of B is corrected.

FIG. 3 shows an electric injection molding machine 1A according to the second embodiment of the present invention. This injection molding machine 1A
Since the drive mechanism section is the same as that of the electric injection molding machine 1 according to the first embodiment shown in FIG. 2, the description of this drive mechanism section is omitted here. The control device 40 according to the second embodiment includes a rotation speed difference calculation circuit 41 instead of the shaft position deviation calculator 31, the pressure deviation calculation circuit 32, and the adder 51 of the control device 30 according to the first embodiment. A rotation speed adder 42 is provided. The rotation speed difference calculation circuit 41 calculates the difference between the rotation speeds of the ball screw shafts 8A and 8B based on the outputs of the encoders 16A and 16B. The rotation speed adder 42 is provided to add the rotation speed difference calculated by the rotation speed difference calculation circuit 41 to the injection speed control operation amount output from the injection speed PID control circuit 33.

The control device 40 operates as follows.
If the rotational speeds of the ball screw shafts 8A and 8B are deviated, the tensile forces acting on the ball screw shafts 8A and 8B become uneven and the smooth movement of the frame 6 is hindered. In the control device 40, in order to avoid this, the rotation speed difference calculation circuit 41
The speed control operation amount output from the injection speed PID control circuit 33 is corrected by the difference in the number of rotations of the ball screw shafts 8A and 8B calculated by. That is, the adder 42
Is a corrected speed control operation for adding the rotational speed difference to the speed control operation amount to correct the speed control operation amount, thereby making the rotational speed difference between the ball screw shafts 8A and 8B zero. You are getting the amount. Then, the corrected speed control operation amount is given to the output circuit 39A.

The output circuit 48A outputs a current corresponding to the former to the motor 11A when the 1/2 pressure control operation amount output from the divider 37 is less than or equal to the corrected speed control operation amount output from the adder 42. When the former is larger than the latter, the current corresponding to the latter is output to the motor 11A. The output circuit 48B outputs 1 / output from the divider 37.
2 When the pressure control operation amount is smaller than the speed control operation amount output from the PID control circuit 33, the current corresponding to the former is output to the motor 11B, and when the former is larger than the latter, the current corresponding to the latter is output to the motor. Output to 11B.

That is, the control device 40 controls the injection pressure P
In the injection filling zone of FIG. 4 in which the pressure control amount output from the ID control circuit 36 is small, and in a partial period of the pressure increasing zone subsequent thereto, a current corresponding to the 1/2 pressure control control amount is output from the output circuits 48A and 48B. Output each. In this case, the injection drive motors 11A and 11B are controlled so that the injection pressure becomes the target injection pressure set by the injection pressure setter 38.

On the other hand, the control device 40 controls the injection pressure PI.
In the second half period of the pressure increasing zone and the pressure maintaining zone of FIG. 4 in which the pressure control amount output from the D control circuit 36 increases, a current corresponding to the corrected speed control control amount output from the adder 42 is output to the output circuit 48A. The output circuit 48B outputs a current corresponding to the pressure manipulated variable output from the injection pressure PID control circuit 36. As a result, in the latter half period of the pressure boosting zone of FIG. 4 and the pressure holding zone subsequent thereto, between the driving means including the motor 11A and the screw shaft 8A and the driving means including the motor 11B and the screw shaft 8B and the like. The unbalance of the rotation speeds of the ball screw shafts 8A and 8B due to the electrical and mechanical variations is corrected.

In the second embodiment as well, when the pair of ball screw shafts 8A and 8B rotate in perfect synchronization, the injection pressure is detected by only one of the pressure detection sensors 18A and 18B. It is possible to detect. That is, as described above, for example, when only the pressure detection sensor 18A is used for detection, the distances between the ball screw shafts 8A and 8B and the central axis of the injection screw 4 are set to l ₁ and l ₂ , respectively. The injection pressure can be detected by multiplying the output of the pressure detection sensor 18A by (l ₁ + l ₂ ) / l ₁ . The present invention is not limited to the above embodiment, and various modifications and changes can be made.

[0044]

The control device for the injection drive unit in the electric injection molding machine according to the present invention comprises a speed control operation amount calculating means for calculating a speed control operation amount for matching the injection speed with the target injection speed, and the injection pressure. Pressure control manipulated variable computing means for computing a pressure control manipulated variable to match the target injection pressure with each of the pressing forces applied to the moving frame by the rotation of the first and second ball screw shafts during the injection process. Pressure deviation output means for detecting deviation, dividing means for dividing the pressure control operation amount into two parts to form first and second 1/2 pressure control operation amounts, and the first 1/2 pressure control operation A correction means for correcting the amount by the deviation of each pressing force; and a current corresponding to the smaller operation amount of the speed control operation amount and the corrected first 1/2 pressure control operation amount. Rotate 1 ball screw shaft A first output means for outputting to the first drive motor, and a current corresponding to a smaller operation amount of the speed control operation amount and the second 1/2 pressure control operation amount, the second ball screw. Second output means for outputting to a second drive motor for rotating the shaft, so as to suppress the pressure deviation by correcting the first ½ pressure control operation amount based on the deviation of each pressing force. I have to. Therefore, during a period in which the speed control operation amount is large during the injection process, a drive unit including the first drive motor, the first ball screw shaft, etc., and a drive unit including the second motor, the second ball screw shaft, etc. It is possible to correct the imbalance of the tensile forces of the first and second ball screw shafts due to the electrical and mechanical variations between the first and second ball screw shafts.

Further, the control device of the injection drive unit in the electric injection molding machine according to the present invention comprises a speed control operation amount calculating means for calculating a speed control operation amount for matching the injection speed with the target injection speed, and the injection pressure. Pressure control manipulated variable calculating means for computing a pressure control manipulated variable for matching the target injection pressure with a target injection pressure, and a rotational speed difference detecting means for detecting a rotational speed difference between the first and second ball screw shafts during the injection process, A dividing unit that divides the pressure control operation amount into two to form first and second 1/2 pressure control operation amounts; a correction unit that corrects the speed control operation amount by the rotational speed difference; Of a current corresponding to the smaller one of the 1/2 pressure control operation amount and the corrected speed control operation amount to the first drive motor for rotating the second ball screw shaft. 1 output means and the second 1 The second pressure control operation amount and the smaller current corresponding to the operation amount of of said speed control operation amount second
Second output means for outputting to the second drive motor for rotating the ball screw shaft of No. 3, and to suppress the rotational speed difference by correcting the first speed control operation amount based on the rotational speed difference. I have to. Therefore, during a period during which the pressure control operation amount is large during the injection process, a drive unit including the first drive motor, the first ball screw shaft, and the like,
First and second due to electrical and mechanical variations between the second motor and the drive means including the second ball screw shaft and the like.
It is possible to correct the imbalance in the rotation speed of the ball screw shaft of.

Further, the control device of the injection drive unit in the electric injection molding machine according to the present invention includes a pressure detection sensor for detecting a tensile force acting on the first ball screw shaft in order to detect the injection pressure. , The distance from the injection cylinder to the first and second ball screw shafts is l ₁ , l ₂ ,
The pressure detected by the pressure sensor is (l ₁ + l ₂ ) / l ₁
And a calculating means for multiplying. Therefore, the injection pressure can be detected by using one pressure detection sensor, which can reduce the cost.

[Brief description of drawings]

FIG. 1 is a plan view partially showing a cross section of an electric injection drive unit in an electric injection molding machine.

FIG. 2 is a block diagram showing an embodiment of a control device for controlling the electric injection drive unit according to the present invention.

FIG. 3 is a block diagram showing another embodiment of a control device according to the present invention for controlling the electric injection drive unit.

FIG. 4 is a graph showing an example of a set injection speed and a set injection pressure with respect to an injection stroke.

[Explanation of symbols]

1 Injection drive 2 fixed frame 3 injection cylinder 4 injection screw 6 moving frames 7 Screw rotation drive motor 8A, 8B Ball screw shaft 16A, 16B encoder 17A, 17B Ball screw nut 18A, 18B Pressure detection sensor 30 control device 31 Screw axis position deviation calculator 32 Pressure deviation calculation circuit 33 Injection speed PID control circuit 34 Injection speed setting device 35 Detection pressure adder 36 Pressure PID control circuit 38 Pressure setting device 39A, 39B output circuit 40 control device 41 Rotation speed difference calculation circuit 42 rpm adder 48A, 48B output circuit 51 adder

Claims (7)

[Claims] 1. An injection cylinder in which an injection screw is fitted so as to move forward and backward, first and second ball screw shafts provided rotatably symmetrically in parallel about an axis of the injection cylinder.
And a fixed frame on which first and second drive motors for respectively rotating and driving the first and second ball screw shafts are mounted, and the first and second ball screw shafts located behind the fixed frame. A moving frame having first and second ball screw nuts respectively screwed to the injection screw, the injection screw, and a third drive motor for rotationally driving the injection screw,
The present invention is applied to an injection drive unit of an electric injection molding machine configured to cause the moving frame to move straight along with the injection screw by the synchronous rotation of the first and second ball screw nuts. A speed control operation amount calculating means for calculating a speed control operation amount for matching the injection speed, a pressure control operation amount calculating means for calculating a pressure control operation amount for matching the injection pressure with a target injection pressure, and an injection process Occasionally, pressure deviation output means for detecting a deviation of each pressing force applied to the moving frame by the rotation of the first and second ball screw shafts, and the pressure control operation amount is divided into two to divide the pressure control operation amount into first and second. Dividing means for forming a 1/2 pressure control operation amount, correction means for correcting the first 1/2 pressure control operation amount by a deviation of each pressing force, the speed control operation amount and the correction amount. First output means for outputting to the first drive motor a current corresponding to the smaller operation amount of the first ½ pressure control operation amount, the speed control operation amount, and the second output device. Second output means for outputting to the second drive motor a current corresponding to a smaller operation amount of the 1/2 pressure control operation amount of the first pressure control operation amount. The control device for the injection drive unit in the electric injection molding machine is characterized in that the pressure deviation is suppressed by correcting the 1/2 pressure control operation amount. 2. The pressure deviation detecting means is configured to detect the pressure deviation based on a difference in rotational speed between the first and second ball screw shafts. A control device for an injection drive unit in the electric injection molding machine described. 3. In order to detect the injection pressure, first and second pressure detection sensors for detecting tensile forces acting on the first and second ball screw shafts, respectively, and the pressure detection sensors for these sensors are detected. The control device for the injection drive unit in the electric injection molding machine according to claim 1, further comprising: an addition unit that adds the pressure. 4. A pressure detection sensor for detecting a tensile force acting on the first ball screw shaft to detect the injection pressure, and from the injection cylinder to the first and second ball screw shafts. _2. The electric injection molding machine according to claim 1, further comprising arithmetic means for multiplying the pressure detected by the pressure sensor by (l ₁ + l ₂ ) / l _{1 with the} distances l ₁ and l _2. Control device of the injection drive unit in. 5. An injection cylinder having an injection screw fitted therein so as to be able to move forward and backward, first and second ball screw shafts rotatably and symmetrically parallel to each other about an axis of the injection cylinder.
And a fixed frame on which first and second drive motors for respectively rotating and driving the first and second ball screw shafts are mounted, and the first and second ball screw shafts located behind the fixed frame. First and second ball screw nuts respectively screwed to the, the injection screw, and a moving frame to which a third drive motor for rotationally driving the injection screw is attached, the first and second ball screws It is applied to the injection drive part of an electric injection molding machine configured to move the moving frame along with the injection screw in a straight line by the synchronous rotation of the nut, and calculates a speed control operation amount for matching the injection speed with the target injection speed. Speed control manipulated variable calculating means, a pressure control manipulated variable calculating means for computing a pressure control manipulated variable for matching the injection pressure with the target injection pressure, and Rotation speed difference means for detecting a rotation speed difference between the first and second ball screw shafts, and a dividing means for dividing the pressure control operation amount into two to form first and second 1/2 pressure control operation amounts. A correction means for correcting the speed control operation amount by the rotation speed difference, and a smaller operation amount of the first 1/2 pressure control operation amount and the corrected speed control operation amount. A first output means for outputting a current to the first drive motor; and a current corresponding to a smaller one of the second 1/2 pressure control operation amount and the speed control operation amount. Second output means for outputting to the second drive motor, and the rotational speed difference is suppressed by correcting the first speed control operation amount based on the rotational speed difference. Control device for injection drive in molding machine. 6. In order to detect the injection pressure, first and second pressure detection sensors for detecting tensile forces acting on the first and second ball screw shafts, respectively, and detection by these sensors. The control device for the injection drive unit of the electric injection molding machine according to claim 5, further comprising: an addition unit that adds the pressure. 7. A pressure detection sensor for detecting a tensile force acting on the first ball screw shaft to detect the injection pressure, and from the injection cylinder to the first and second ball screw shafts. 6. The electric injection molding machine according to claim 5, further comprising arithmetic means for multiplying the pressure detected by the pressure sensor by (l ₁ + l ₂ ) / l _{1 with the} distances l ₁ and l _2. Control device of the injection drive unit in.